U.S. patent application number 10/068863 was filed with the patent office on 2002-10-17 for oxide magnetic material and coil part using the same.
This patent application is currently assigned to TDK CORPORATION. Invention is credited to Saito, Yutaka, Yokoyama, Ryo.
Application Number | 20020148995 10/068863 |
Document ID | / |
Family ID | 18899518 |
Filed Date | 2002-10-17 |
United States Patent
Application |
20020148995 |
Kind Code |
A1 |
Yokoyama, Ryo ; et
al. |
October 17, 2002 |
Oxide magnetic material and coil part using the same
Abstract
An oxide magnetic material is made of a composition containing
46.0 to 50.0 mol % of Fe.sub.2O.sub.3, 20.0 to 30.0 mol % of ZnO,
7.1 to 10.0 mol % of CuO, 1.0 or less mol % (excluding 0 mol %) of
MgO, and a residual of NiO. A coil part has a core made of this
oxide magnetic material.
Inventors: |
Yokoyama, Ryo; (Tokyo,
JP) ; Saito, Yutaka; (Tokyo, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
TDK CORPORATION
Tokyo
JP
|
Family ID: |
18899518 |
Appl. No.: |
10/068863 |
Filed: |
February 11, 2002 |
Current U.S.
Class: |
252/62.56 |
Current CPC
Class: |
C04B 35/265 20130101;
H01F 1/344 20130101; H01F 17/045 20130101; H01F 27/292 20130101;
H01F 27/027 20130101 |
Class at
Publication: |
252/62.56 |
International
Class: |
C04B 035/26 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 13, 2001 |
JP |
2001-036214 |
Claims
What is claimed is:
1. An oxide magnetic material comprising: a composition containing
46.0 to 50.0 mol % of Fe.sub.2O.sub.3, 20.0 to 30.0 mol % of ZnO,
7.1 to 10.0 mol % of CuO, 1.0 or less mol % of MgO, and a residual
of NiO.
2. The oxide magnetic material according to claim 1, wherein said
composition contains 0.1 to 0.75 mol % of MgO.
3. A coil part comprising: a core made of an oxide magnetic
material including a composition containing 46.0 to 50.0 mol % of
Fe.sub.2O.sub.3, 20.0 to 30.0 mol % of ZnO, 7.1 to 10.0 mol % of
CuO, 1.0 or less mol % of MgO, and a residual of NiO.
4. The oxide magnetic material according to claim 3, wherein said
composition contains 0.1 to 0.75 mol % of MgO.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an oxide magnetic material
for cores of a choke coil and an inductor, and a coil part using
this oxide magnetic material for its core.
[0003] 2. Description of the Related Art
[0004] In recent years, downsizing and weight reduction of various
kinds of electronic apparatus have been advanced exponentially. In
accordance therewith, there has grown rapidly a demand for smaller
size and higher performance of electronic parts for electric
circuits of such electronic apparatus.
[0005] As a magnetic material for a power supply choke coil which
is one of such electronic parts, Ni--Zn based ferrite is often used
for the following reasons. That is, Ni--Zn based ferrite is so high
in resistivity that it can be used in the form of direct winding.
Thus, the power supply choke coil can be made small in size and low
in cost. In addition, Ni--Zn based ferrite is so high in Curie
temperature that the temperature characteristics of saturated
magnetic flux density Bs are excellent.
[0006] However, the saturated magnetic flux density Bs of Ni--Zn
based ferrite is generally lower than that of Mn--Zn based ferrite.
Therefore, as a magnetic material used for a power supply choke
coil, Ni--Zn based ferrite has been requested to have higher Bs. As
well as such a request, there has been another request for
improvement and addition of other properties required for
manufacturing cores as power supply choke coil parts.
[0007] Specifically, the following requests have been made:
[0008] (1) Increase of saturated magnetic flux density Bs so as not
to be saturated against a high magnetic field generated by
application of a high current, that is, so as to improve DC
superimposition characteristics;
[0009] (2) Increase initial magnetic permeability .mu.i to obtain
desired inductance even if the number of wire turns is reduced to
thereby reduce a DC resistance value for the purpose of saving
power consumption;
[0010] (3) Improvement of the temperature characteristics of the
initial magnetic permeability .mu.i so as to keep excellent DC
superimposition characteristics even in a high operating
temperature range; and
[0011] (4) Prevention of inductance from changing due to resin
molding when electronic parts are surface-mounted, that is, to keep
stress-resisting characteristics excellent.
[0012] In addition, about the properties of a magnetic material for
power supply inductors, there have been requests similar to those
of the power supply choke coils.
[0013] In response to these requests, Japanese Patent Laid-Open No.
Hei. 6-295811 discloses an oxide soft magnetic material obtained by
adding Mo oxide not higher than 3,000 ppm in terms of MoO.sub.3 to
a basic composition containing 48 to 50 mol % of Fe.sub.2O.sub.3,
15 to 25 mol % of ZnO, 2.5 or less mol % of CuO, 22 to 37 mol % of
NiO, and a residual of unavoidable impurities. The same publication
says that high Bs and high .mu.i can be realized by setting the
composition of an oxide soft magnetic material within the
above-mentioned range. However, the same publication says nothing
about the change of inductance when external stress is applied.
[0014] In addition, Japanese Patent Laid-Open No. Sho. 63-275104
discloses an oxide magnetic material characterized in that 0.1 to
3.0 wt % of Sb.sub.2O.sub.3 is added to Ni--Zn based ferrite
composed of 40 to 55 mol % of Fe.sub.2O.sub.3, 5 to 50 mol % of
NiO, 0 to 20 mol % of CuO, and 0 to 30 mol % of ZnO. According to
the same publication, an oxide magnetic material satisfying
magnetic permeability, temperature characteristics and compression
characteristics simultaneously can be provided by setting the
composition of the oxide magnetic material within the
above-mentioned range. The same publication indeed refers to the
compression characteristics, but discloses no specific data about
the compression characteristics.
[0015] Japanese Patent Laid-Open No. Hei. 5-3112 discloses an oxide
magnetic material characterized in that Ni--Cu--Zn based ferrite is
adopted as a main component, and any one kind of Nb.sub.2O.sub.5
ranging from 0.2 to 0.8 wt %, Ta.sub.2O.sub.5 ranging from 0.3 to
1.2 wt % and MoO.sub.3 ranging from 0.15 to 1.35 wt % is added as a
subsidiary component to this main component.
[0016] According to the same publication, an oxide magnetic
material having high initial magnetic permeability and a low
temperature coefficient of the initial magnetic permeability can be
provided by making the oxide magnetic material have the
above-mentioned composition. However, the same publication
discloses nothing about saturated magnetic flux density Bs and
stress-resisting characteristics. It cannot be said that the oxide
magnetic material having this composition satisfies all the
properties required of used for a power supply choke coil and a
power supply inductor.
[0017] In addition, Japanese Patent Laid-Open No. Hei. 1-103953
discloses a ferrite material characterized in that 0.05 to 2.0 wt %
of Bi.sub.2O.sub.3 is contained in Ni--Cu--Zn based ferrite which
is composed of 40 to 50 mol % of Fe.sub.2O.sub.3, 20 to 35 mol % of
ZnO, 3 to 10 mol % of Cuo, and a residual of NiO, and in which at
most 1/2 of NiO is substituted by MgO and/or (1/4)
(Li.sub.2O+Fe.sub.2O.sub.3) and/or Mn oxide. According to the same
publication, a ferrite material having high initial magnetic
permeability .mu.i, high saturated magnetic flux density Bs and
high strength and superior in resistance to thermal shock can be
provided by making the ferrite material have the above-mentioned
composition. The same publication indeed refers to mechanical
strength of the ferrite material, but says nothing about
compression characteristics of the initial magnetic permeability,
that is, stress-resisting characteristics.
[0018] Japanese Patent Laid-Open No. Hei. 3-93667 discloses a
magnetic material characterized in that 0.1 to 12 wt % of
Bi.sub.2O.sub.3 and 0.05 to 4.0 wt % of SiO.sub.2 are contained in
a spinel type composition which is composed of 25 to 40 mol % of
Fe.sub.2O.sub.3, 0 to 20 mol % of ZnO, and a residual of NiO and
CuO, and in which NiO is substituted by 0.1 to 20 mol % of MgO.
According to the same publication, a magnetic material excellent in
compression characteristics and magnetic field characteristics can
be provided by making the magnetic material have the
above-mentioned composition. However, initial magnetic permeability
.mu.i of the magnetic material shown in Example of the same
publication is approximately in a range of from 5 to 10, and the
same publication says nothing about saturated magnetic flux density
Bs. Therefore, it cannot be said that this magnetic material
satisfies all the properties required of cores for a power supply
choke coil and a power supply inductor.
[0019] Japanese Patent Laid-Open No. Hei. 10-335131 discloses an
oxide magnetic material characterized in that Ni--Mg--Cu--Zn based
ferrite is adopted as a main component, and 2.16 to 3.95 wt % of
PbO, 0.80 to 1.63 wt % of SiO.sub.2 and 1.4 to 3.0 wt % of
Nb.sub.2O.sub.3 are contained as subsidiary components in addition
to this main component, or 0.01 to 0.10 wt % of Co.sub.3O.sub.4 is
further contained in addition to the subsidiary components.
According to the same publication, a magnetic material having high
initial magnetic permeability .mu.i and a low temperature
coefficient can be provided by making the magnetic material have
the above-mentioned composition. However, initial magnetic
permeability .mu.i of the magnetic material shown in Example of the
same publication is approximately in a range of from 18 to 69, and
the same publication says nothing about saturated magnetic flux
density Bs and stress-resisting characteristics. Therefore, it
cannot be said that this magnetic material satisfies all the
properties required of cores used for a power supply choke coil and
a power supply inductor.
[0020] In addition, Japanese Patent Laid-Open No. 2000-306719
discloses an oxide magnetic material which is composed of 48 to 50
mol % of Fe.sub.2O.sub.3, 20 to 32 mol % of ZnO, 3 to 7 mol % of
CuO and a residual of NiO, and in which 0 to 5 mol % of ZnO is
substituted by MgO, while the average crystalline grain size of a
sintered product is not smaller than 5 .mu.m. According to the same
publication, an oxide magnetic material having high specific
resistance and low loss can be provided by making the magnetic
material have the above-mentioned composition. However, the same
publication says nothing about the change of inductance when
external stress is applied, that is, stress-resisting
characteristics. Therefore, it cannot be said that this magnetic
material satisfies all the properties required of cores used for a
power supply choke coil and a power supply inductor, particularly
for a resin-mold type power supply choke coil and a resin-mold type
power supply inductor.
[0021] As described above, in the conventional magnetic materials,
there was no magnetic material high in saturated magnetic flux
density Bs and initial magnetic permeability .mu.i, excellent in
temperature characteristics of the initial magnetic permeability
.mu.i and excellent in stress-resisting characteristics.
SUMMARY OF THE INVENTION
[0022] It is therefore an object of the present invention to
provide an oxide magnetic material high in saturated magnetic flux
density Bs and initial magnetic permeability .mu.i, excellent in
temperature characteristics of the initial magnetic permeability
.mu.i and excellent in stress-resisting characteristics, and a coil
part having a core using the same oxide magnetic material.
[0023] An oxide magnetic material according to claim 1 is
characterized by being made of a composition containing 46.0 to
50.0 mol % of Fe.sub.2O.sub.3, 20.0 to 30.0 mol % of ZnO, 7.1 to
10.0 mol % of CuO, 1.0 or less mol % (excluding 0 mol %) of MgO,
and a residual of NiO.
[0024] A coil part according to claim 2 is characterized by
including a core made of an oxide magnetic material according to
claim 1.
[0025] By setting the composition within the above-mentioned range,
the oxide magnetic material according to the present invention can
be made high in saturated magnetic flux density Bs, high in initial
magnetic permeability .mu.i, excellent in temperature
characteristics of the initial magnetic permeability .mu.i and
excellent in stress-resisting characteristics.
[0026] Here, the reason why the respective components of the
composition are set as mentioned above is just as follows. When
Fe.sub.2O.sub.3 of the respective components is lower than 46.0 mol
%, the density of a sintered product lowers. Then, in the range
where Fe.sub.2O.sub.3 has exceeded its stoichiometric composition,
the density of a sintered product and the specific resistance as a
core begin to lower due to precipitation of Fe.sub.3O.sub.4 in
firing in the air. Such precipitation appears conspicuously in the
range where Fe.sub.2O.sub.3 exceeds 50.0 mol %.
[0027] In addition, when CuO is lower than 7.1 mol %, the sintering
characteristics of the magnetic material deteriorate so that the
density of a sintered product lowers. Thus, the physical strength
of the core is lowered. On the other hand, when CuO exceeds 10.0
mol %, the specific resistance of the core is lowered.
[0028] In addition, when ZnO is lower than 20.0 mol %, the initial
magnetic permeability .mu.i is lowered. On the other hand, when ZnO
exceeds 30.0 mol %, the Curie temperature becomes low, causing a
problem in practical use.
[0029] In addition, when MgO is contained, an excellent value can
be obtained in each of the saturated magnetic flux density Bs, the
temperature characteristics of the initial magnetic permeability
.mu.i and the stress-resisting characteristics. On the other hand,
when MgO is not contained, it is difficult to make all of these
three properties excellent at the same time. When this MgO exceeds
1.0 mol %, the saturated magnetic flux density Bs lowers, and the
temperature characteristics of the initial magnetic permeability
.mu.i and the stress-resisting characteristics also
deteriorate.
[0030] In addition, according to the present invention, NiO is
contained as a residual for the main components. This is a residual
after adjusting various properties with other components. Here,
when NiO is not contained, the specific resistance lowers, and the
stress-resisting characteristics also deteriorate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a partially see-through perspective view showing
an embodiment of a choke coil according to the present
invention.
[0032] FIG. 2 is a partially see-through perspective view showing
an embodiment of an inductor according to the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] A magnetic material according to the present invention is
made of the above-mentioned composition. For example, the magnetic
material is manufactured as follows. Iron oxide, copper oxide, zinc
oxide, magnesium oxide and nickel oxide are basically used as raw
materials for the respective components. As for magnesium, other
magnesium compounds such as Mg(OH).sub.2 and the like may be used
so that the constitutive ratio of magnesium in terms of MgO is set
within the above-mentioned range in a magnetic material obtained
finally. The respective raw materials are mixed so that a final
composition has the above-mentioned composition ratio.
[0034] Next, the mixture is calcined. Normally, the calcination may
be carried out in the air. It is preferable that the calcination
temperature is set to be in a range of from 800.degree. C. to
1,100.degree. C., and the calcination time is set to be in a range
of from 1 hour to 3 hours.
[0035] Next, the obtained calcined product is ground to have a
predetermined grain size by a ball mill or the like. After the
calcined product has been ground, a proper quantity of suitable
binder such as polyvinyl alcohol or the like is added to the
calcined product, which is then formed into a predetermined
shape.
[0036] Next, the formed element is fired. Normally the firing may
be carried out in the air. It is preferable that the firing
temperature is set to be approximately in a range of from
900.degree. C. to 1,200.degree. C., and the firing time is set to
be in a range of from 2 hours to 5 hours.
[0037] A coil part according to the present invention can be
obtained as follows. That is, the above-mentioned magnetic material
according to the present invention is processed in a core having a
predetermined shape. Then, necessary winding is applied to the
core, and subjected to resin molding or the like in accordance with
necessity. Incidentally, in order to form the core into a
predetermined shape, a method of forming before firing may be
adopted as described previously, or a method of processing after
firing may be adopted.
[0038] FIG. 1 is a partially see-through perspective view showing a
constructional example of a choke coil using ferrite cores (a drum
core 1 and a ring core 2) made of a magnetic material according to
the present invention. In FIG. 1, a winding wire 3 is wound around
the drum core 1. Resin 6 is filled between the drum 1 with the
winding wire 3 wound thereon and the ring core 2, while these cores
1 and 2 are bonded onto a base 4. A pair of terminal electrodes 5
are fixed to the base 4, and opposite ends of the winding wire 3
are connected to the respective terminal electrodes 5.
[0039] FIG. 2 is a partially see-through perspective view showing a
constructional example of a chip inductor using a ferrite core made
of a magnetic material according to the present invention. The chip
inductor in this embodiment has a drum type core 7, a winding wire
8, terminal electrodes 9, and a mold material 10. The core 7 is
formed from the ferrite according to the present invention and has
large-diameter collar portions on its opposite ends. The winding
wire 8 is wound around a trunk portion of the core 7. The terminal
electrodes 9 connect end portions of the winding wire 8 to an
external electric circuit, and fixes the core 7 into resin (the
mold material 10). The mold material 10 is provided to cover the
outside of these members.
[0040] The configuration of a choke coil or a chip inductor is not
limited to the illustrated embodiments, but various forms can be
adopted. For example, a choke coil may be configured so that resin
is poured into a pot core with a center leg, and a plate-like
ferrite core is combined to cap an opening portion of the pot core
so as to enclose the resin. In addition, for example, an inductor
may be configured so that a coil assembly in which a winding wire,
a lead wire, etc. are provided on a core is inserted into a
box-shaped resin case, and an opening portion is sealed with a mold
material.
[0041] Raw materials of respective components were weighed to have
each composition ratio shown in Table 1, and mixed by a ball mill
for 5 hours. Incidentally, Samples 1 to 8 in Table 1 are examples
within the composition range of the present invention, while
Samples 9 to 14 are comparative examples out of the composition
range of the present invention.
[0042] The mixture obtained as described above was calcined in the
air at 900.degree. C. for 2 hours, then mixed and ground by the
ball mill for 20 hours. The ground mixture was dried, and 1.0 wt %
polyvinyl alcohol was added thereto. After that, the mixture was
pressed and formed at the pressure 100 kPa so as to obtain a
rectangular formed element measuring 50 mm by 10 mm by 7 mm and a
toroidal formed element measuring 20 mm in outer diameter, 10 mm in
inner diameter and 5 mm in height. These formed elements were fired
in the air for 2 hours at each temperature shown in Table 1 so as
to obtain a rectangular core sample and a toroidal core sample made
of a magnetic material.
[0043] A wire was wound around a center portion of the
above-mentioned rectangular core sample by 14 turns. After that,
uniaxial compressive force was applied to this at a constant speed,
and an inductance value at this time was measured successively. The
ratio of inductance change was calculated from the obtained
measured values. The ratio .DELTA.L/L of change in inductance value
when uniaxial compressive force of 50 kPa was applied is shown in
Table 1. Here, L designates inductance before the compression, and
.DELTA.L designates a variation of inductance caused by the
compression, that is, a value obtained by subtracting the
inductance before the compression from the inductance at the time
of the compression.
[0044] Incidentally, the uniaxial compression was carried out by a
load tester made by Aikoh Engineering Co., Ltd. (measuring stand
MODEL 1321, measuring amplifier MODEL 1011 CREEP, and load cell
MODEL 3800). The inductance values were measured by a precision LCR
meter 4284A made by Hewlett-Packard Company.
[0045] In addition, a wire was wound around the toroidal core
sample by 20 turns. After that, an inductance value was measured by
the above-mentioned LCR meter, and initial magnetic permeability
.mu.i at 100 kHz and relative temperature coefficients
.alpha..mu.ir in the range of from -20.degree. C. to 20.degree. C.
and in the range of from 20.degree. C. to 60.degree. C. were
obtained in accordance with Equation 1. Incidentally, in Equation
1, T.sub.1 and T.sub.2 designate temperatures with which the
magnetic permeability was measured, respectively, and .mu.i.sub.1
and .mu.i.sub.2 designate initial magnetic permeability at the
temperatures T.sub.1 and T.sub.2 respectively.
1 TABLE 1 Firing Properties Constitutive Ratio (mol %) Temperature
Bs .alpha..mu.ir (-20 to 20.degree. C.) .alpha..mu.ir (20 to
60.degree. C.) .DELTA.L/L Sample No. Fe.sub.2O.sub.3 NiO CuO ZnO
MgO (.degree. C.) .mu.i (mT) (ppm/.degree. C.) (ppm/.degree. C.)
(%) 1 48.50 17.00 7.90 26.50 0.10 1030 566 408 8.7 7.2 -2.2 2 48.50
17.00 9.00 25.25 0.25 1030 504 415 9.6 5.9 -1.8 3 48.50 17.00 8.00
26.25 0.25 1060 580 410 8.4 4.7 -1.8 4 48.25 17.00 8.00 26.25 0.50
1060 566 407 8.5 4.5 -1.8 5 48.25 17.50 7.50 26.25 0.50 1090 574
408 9.5 7.6 -2.2 6 48.50 17.50 7.50 26.25 0.25 1060 603 410 9.1 7.8
-2.6 7 48.50 17.00 7.50 26.25 0.75 1030 559 406 8.1 5.1 -2.5 8
48.75 17.00 8.00 25.25 1.00 1060 530 405 9.3 6.8 -2.7 9
(Comparative) 46.75 18.50 9.00 25.75 1030 383 400 8.6 3.5 -1.0 10
(Comparative) 48.75 17.00 9.00 25.25 1030 475 432 11.5 11.5 -3.0 11
(Comparative) 48.75 18.75 6.00 26.50 1090 590 413 9.8 12.4 -3.2 12
(Comparative) 48.50 17.00 8.00 26.50 1060 577 411 11.1 12.7 -2.5 13
(Comparative) 48.75 17.00 7.00 25.25 2.00 1060 513 404 10.7 11.9
-3.0 14 (Comparative) 48.75 17.00 6.00 25.25 3.00 1090 501 401 12
13.9 -3.3
[0046] 1 i r = i 2 - i 1 i 1 2 1 T 2 - T 1 [ Equation 1 ]
[0047] In addition, a secondary winding wire was wound by 40 turns
around the above-mentioned toroidal sample used for measurement of
the initial magnetic permeability .mu.i and the relative
temperature coefficients .alpha..mu.ir. After that, saturated
magnetic flux density Bs was measured by a B.H curve tracer made by
Riken Denshi. Co., Ltd, while a magnetic field of 4 kA/m was
applied. These results are shown in Table 1.
[0048] As is understood from Table 1, in Samples 1 to 8 in which
Fe.sub.2O.sub.3, ZnO and CuO are within the above-mentioned
composition range according to the present invention, NiO is
contained, and 1 or less mol % of MgO is contained, a high value
not lower than 500 can be obtained as the initial magnetic
permeability .mu.i, and a high value not lower than 400 mT can be
also obtained as the saturated magnetic flux density Bs. In
addition, in these Samples 1 to 8, the relative temperature
coefficient (.alpha..mu.ir of inductance can be controlled to be
lower than 10 in the temperature range of from -20.degree. C. to
20.degree. C. and in the temperature range of from 20.degree. C. to
60.degree. C. In addition, in these Samples 1 to 8, the ratio
.DELTA.L/L of change in inductance value is higher than -3.0. Thus,
excellent stress-resisting characteristics could be obtained.
Particularly in consideration of the stress-resisting
characteristic (the ratio of change in inductance value)
.DELTA.L/L, it is more preferable that the MgO content by
percentage is in a range of from 0.1 mol % to 0.75 mol %.
[0049] On the other hand, in the case of Samples 9 to 14 in which
the MgO content is zero or not lower than 2 mol %, the relative
temperature coefficient .alpha..mu.ir of inductance reaches a value
exceeding 10 in at least one or both of the temperature range of
from -20.degree. C. to 20.degree. C. and the temperature range of
from 20.degree. C. to 60.degree. C. In addition, in Samples 10 to
14, absolute values of the stress-resisting characteristic
.DELTA.L/L increases to 3.0 or more.
[0050] As has been described in detail above, a magnetic material
according to the present invention is high in saturated magnetic
flux density Bs and initial magnetic permeability .mu.i, excellent
in temperature characteristics of the initial magnetic permeability
.mu.i and also excellent in stress-resisting characteristics. That
is, the magnetic material can satisfy all the properties required
of a magnetic material for cores of a power supply choke coil and a
power supply inductor. Accordingly, by using the magnetic material
according to the present invention, it is possible to provide a
high-quality power supply choke coil and a high-quality power
supply inductor.
* * * * *